The purpose of this study was to examine the use of percentile schedules as a method of quantifying the shaping procedure in an educational setting. We compared duration of task engagement during baseline measurements for 4 students to duration of task engagement during a percentile schedule. As a secondary purpose, we examined the influence on shaping of manipulations of the number of observations used to determine the criterion for reinforcement (the m parameter of the percentile formula). Results showed that the percentile formula was most effective when a relatively large m value (20 observations) was used. (Contains 2 tables and 2 figures.)